A newly created Cloud Router BGP session stays in the TCP CONNECT state and never transitions to ESTABLISHED. What is the most likely immediate cause?
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Correct answer: A firewall between on‑prem and Google Cloud is blocking TCP port 179..
Why this is the answer
BGP (Border Gateway Protocol) uses TCP port 179 for establishing and maintaining peering sessions. If a BGP session is stuck in the TCP CONNECT state, it indicates that the TCP handshake is not completing. The most common reason for this is a firewall blocking the necessary port. If TCP port 179 is blocked, the BGP session cannot transition to the ESTABLISHED state. Incorrect options: Different ASNs would prevent the BGP session from becoming ESTABLISHED, but typically after the TCP session has been established. BFD (Bidirectional Forwarding Detection) operates over UDP and is used for fast failure detection, not for establishing the initial TCP BGP session. Cloud Routers are global resources; their location relative to an on-prem router does not dictate TCP session establishment in the way described.
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